The Ordovician–Silurian tectonic evolution of the northeastern margin of the Tarim block, NW China: Constraints from detrital zircon geochronological records

Abstract

The northeastern margin of the Tarim block is a key tectonic-unit for understanding the evolution processes and geodynamic mechanisms of basin–range coupling between the Paleo-Asian tectonic realm to the north and the Tarim block to the south during the Paleozoic period. Four Upper Ordovician–Silurian sandstone samples were collected from the Tabei and Quruqtagh areas for measuring the detrital zircon U–Pb dating and Hf isotopic compositions, with an aim to decipher the provenances and elucidate the tectonic implications. The results show that all the sandstone samples yield evident detrital zircon U–Pb age groups of ca. 1100–720Ma and ca. 2100–1700Ma, demonstrating that the Tarim block was once a part of the Rodinia and Columbia supercontinents during the Neoproterozoic and the Paleoproterozoic, respectively. Remarkably, the Upper Ordovician sandstone sample from the Tabei area yields a higher proportion in age group of ca. 1100–900Ma than that of ca. 860–720Ma, whilst the Lower Silurian sample yields the opposite result. The former and the latter age groups aforementioned are consistent with the age patterns of the tectono-thermal events in the Central Tianshan microcontinent and the Tarim block, respectively. Combined with valuable igneous rock information, it is indicative that the Central Tianshan microcontinent drifted away from the proto Tarim block (with attachment of the Central Tianshan microcontinent) most likely at the Early Silurian. The Upper Silurian sandstone in the South Quruqtagh area yield massive detrital zircon U–Pb ages with a peak age of ca. 450Ma, combining the Late Ordovician magmatic rocks reported from the Central Tianshan and northeastern Tarim margin, which suggests that there was a broad magmatic arc along the northeastern proto Tarim margin during the Late Ordovician. The opening of the South Tianshan Ocean began in the Early Silurian and continued in the Late Silurian, leaving a remanent magmatic arc along northeastern Tarim margin. Reliable Devonian intrusive/volcanic rocks and detrital zircons ages indicate a southward subduction of the South Tianshan Ocean beneath the northeastern Tarim during the Devonian.